Today, conventional vapor compression air conditioning systems are the most common methods of controlling humidity in an environment. Such systems generally pass a humid air stream over a cooler where water vapor condenses out of the humid air before it exits the system in a liquid phase. In most instances, the condensation of water vapor from humid air is driven by a temperature gradient. These systems typically use pumps, fans, and other similar devices to deliver the humid air stream to the system, remove the condensed water vapor from the system, and recirculate the less humid air back into the environment. As a consequence of these features, these systems consume large amounts of energy.
The challenge of controlling moisture levels is particularly difficult in a confined environment, such as airplanes, space shuttles, and submarines, where there is limited to no circulation of air, large volumes of air to dehumidify, and energy consumption is high and costly. Conventional systems also present challenging issues relating to design capacity. As the amount of humidity to be removed from an environment increases, the size of the system must increase. This increase in size results in a corresponding increase in costs. Another challenge is maintaining moisture levels in environments with high humidity within the American Society of Heating, Refrigerating, and Air-Conditioning Engineers' recommended range of 45% relative humidity (or even lower) to 65% relative humidity.